Formation And Evolution Mechanisms Of Tropical Components In The Sino-Himalaya Flora

Species are extremely rich and the geographical components are complex in the Sino-Himalaya flora that is always viewed as the significant center of the diversification and distribution of the flora of East Asia,even the temperate flora of Northern Hemisphere.Tropical component is an important part of the geographical component of the Sino-Himalaya flora.Study on the formation and evolutionary history of the tropical component is instrumental in understanding the origination and formation of distribution pattern of the floristic component,which will contribute to answer the significant theoretical questions of biogeographical origin of plant diversity in the region.This study analyzes the mechanisms of origination and formation of biogeographical pattern of Urticeae(Urticaceae)and Berchemia(Rhamnaceae),and reveals the origination and formation of modern geographical pattern of the tropical component of the Sino-Himalaya flora,including pantropic,tropical Asia and America disjuncted,tropical Asia to tropical Australasia,tropical Asia to tropical Africa and tropical Asia.Detailed results are as follows:1.Biogeography of UrticeaeThe tribe Urticeae include 12 genera and ca.200 species,constituting a diverse and cosmopolitan plant clade centered in tropical Asia,Africa,and South America.Based on the nuclear ITS and four plastid DNA regions of 115 Urticeae accessions representing 91 species,the phylogeny and ancestral areas were reconstructed and the divergence times were inferred in this tribe.In this study,the monophyly of many genera of Urticeae were well supported.The stem and crown group of this tribe likely originated in tropical Asia.Migration events to Eurasia,South America and Africa occurred mainly during the Oligocene and Miocene.And long-distance dispersal events,including dispersals from Asia to Hawaii or Australasia,were inferred to have mainly occurred from the Miocene onwards.The origination of tropical component related to Urticeae are as follows:1)The stem group of pantropic Laportea II originated in tropical Asia in 53.70 Ma,and then existed throughout tropical Asia,Eurasia and Africa during the late Oligocene,with subsequent dispersal / vicariance across the globe.2)The stem group of Dendrocnide with the disjunct distribution of tropical Asia and tropical Australasia originated in tropical Asia to tropical Australasia in 23.66 Ma,and then was affected by vicariance during the late Miocene.3)The stem group of Girardinia with the disjunct distribution of tropical Asia to tropical Africa originated in tropical Asia in 50.11 Ma,and then migrated to Eurasia and Africa from Miocene on.4)The stem group of Poikilospermum distributed in tropical Asia originated in tropical Asia in 19.34 Ma,and its later diversification was likely related to the uplift of Qinghai-Tibetan Plateau(QTP)and the establishment and enhancement of Asian monsoons.2.Biogeography of BerchemiaBerchemia,comprising 32 species,is distributed predominantly in tropical regions of east to southeast Asia,North America and Africa.Based on the two nuclear and three plastid DNA regions of 34 Berchemia accessions representing 21 species,the phylogeny and ancestral areas were reconstructed and the divergence times were inferred in this genus.Our results indicated that the Berchemia is not monophyletic and two species of Africa should be excluded from this genus.The core Berchemia likely originated in Western Tethys during the middle Eocene,then formed the tropical Asia and tropical America disjunction from the Oligocene on and diversified in Asia from the early Miocene on.The formation of disjunct distribution and diversification of the core Berchemia probably resulted from a mixture of geologic events,such as the close of Tethys Ocean,disappearance of NALB and uplift of QTP,and climatic events,such as establishment and enhancement of Asian monsoons.3.Formation and diversification of the tropical component in the Sino-Himalaya floraBased on the above 5 taxa of the tropical component of the Sino-Himalaya flora,this study adds 16 clades of the tropical component from previous study to understand comprehensively the formation and diversification of the tropical component in the Sino-Himalaya flora.In the origin place of stem group of the above 21 clades,the origin place of 19 clades were related to Asia,the origin place of 14 clades of which were all tropical Asia.In the age of stem group of the above21 clades,including 3 taxa with the unknown age,the age of 17 clades were older than 23 Ma and the age of Poikilospermum was 19.34 Ma.Meanwhile,the mean and median ages of stem group of the above 18 clades were 48.48 ± 4.24 Ma and 49.95 Ma,respectively.Thus,it was finally inferred that the tropical component in the Sino-Himalaya flora originated in several places,but mainly in tropical Asia;and its origin time was always ancient and in Paleogene;and its formation and diversification were likely associated with long-distance dispersal,migration /vicariance.Additionally,based on the Plants of the world,the latest relevant literatures and the previous areal-types' delimiting scheme and method of the world families of seed plants,this study rejudged the areal-types of these families.Our results showed a total of 427 world families of seed plants were classified into 16areal-types and 51 subtypes.Compared to previous studies,the distribution patterns of 118 families changed in the 427 families,which mainly resulted from the change of phylogenetic relationship of these families.